For example, the nucleus of a cell is an organelle that maintains the integrity of genes and controls cell activity by regulating gene expression. Lysosomes are organelles that digest food particles, worn out organelles, and viruses andbacteria. Mitochondria generate most of a cell's supply of ATP, among other functions. Among other structures known as organelles are vacuoles, peroxisomes, and chloroplasts.
Some subcellular structures commonly called organelles, such as ribosomes, are not actually an organelle under the more restrictive definition of being enclosed within a separate membrane. Ribosomes, being strictly particulate, do not include such a membrane. However, the term organelle sometimes is used in the less restrictive sense of any distinct, subcellular structural unit. Thus, ribosomes are at times described as "non-membranous organelles" or the nucleolus as a "nuclear membraneless organelle."
The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the nameorganelle, the suffix -elle being a diminutive). Just as organs provide a particular function for the body, organelles provide a particular function for cells. This harmony is seen on each level of an organism, as cells work together as part of tissues, tissues as part of organs, and organs as part of organ systems. An analogy might be made with a harmonious human society, whereby individuals contribute to their families (as organelles to cells), their families to their communities (as cells to tissues), communities to societies (as tissues to organs), societies to their nations (as organs to organ systems), and their nations to the world (as organ systems to the body), and in turn each would be benefited by those larger entities.
Although viewed as whole, the human body is actually made up of ten different systems. Each of these systems plays a vital part in the health and well being of the entire body.
1. Skeletal system- The skeletal system is the framework of the body. It is what gives the body its basic shape, while protecting the delicate internal tissues and organs. The joints of the skeletal system act as levers that are attached to various . The elbows, knees, ankles are just a few examples of these levers. Another use of the skeleton system is as a storage area for in case there is an inadequate amount available in the . A vital role of this system is also the production of red .
2. Muscular system- There are three types of muscle tissue that is included in this system, skeletal, cardiac and visceral.
Skeletal muscles are voluntary muscles that work with the connective tissues to allow the body to move. Voluntary simply means the muscles respond to impulses from the that are a result of your desire to move.
Cardiac muscles are those that form the bulk of the heart’s wall. They are known as the myocardium and are involuntary muscles. It is due to the cardiac muscles that the contractions know as heartbeats occur.
Visceral muscles are also involuntary. They are known as the smooth muscle that is the walls of the viscera. Examples of visceral muscles are those that help move food along in the digestive tract, veins and as well as the tubular structures of the urinary tract.
3. Digestive system – The digestive system is comprised of all the organs that help break down food into a useable substance for the body. It includes the mouth, teeth, tongue, esophagus, stomach, duodenum, small and large intestines, colon, and rectum. It will also include accessory organs like the salivary glands, liver, gallbladder, pancreas and spleen.
4. Circulatory system- The circulatory system is a closed system whose main function is to carry blood to all parts of the body. It is made up of the heart, arteries and systemic arterioles which carry oxygenated blood from the heart to the cells in the body as well as the systemic capillaries and veins which carry deoxygenated blood from the body back to the heart.
5. Respiratory system- The respiratory system is comprised of the lungs and the passages that lead to and from them. This system begins at the nostrils and will include the nasal cavities, sinuses, pharynx, larynx (voice box) and trachea (windpipe). Just before entering the lungs, the trachea branches into two bronchi that lead into the lungs. It is interesting to note that the right bronchus, which leads into the right lung, is noticeably larger than the left one. If a foreign object is accidentally inhaled, it is more likely to enter the right lung.
It is in the lungs that oxygen from the outside meets the blood by way of the thin tissues in the lungs. As the oxygen passes through the bronchi, it then enters the bronchial tubes. When viewed from a cross section of the lungs, the bronchial tubes will resemble the limbs of a tree that grow progressively smaller with each branch. At the end of each of the tiniest branches of the bronchial tubes is a cluster of air sacs that resemble a bunch of grapes. Each of the alveoli is made up of a one-cell layer of flat cells and it is through these cells that the actual oxygen/blood mixture is done.
6. Integumentary () system- The integumentary system is the largest of all systems. It is comprised of the skin, hair, nails as well as the sweat and oil glands. It functions as a protective covering for the underlying tissues against drying and invasion by toxins or pathogenic organisms. The skin is also responsible for regulating body temperature.
The skin is made up of three distinct tissue layers. The epidermis is the outermost layer and is made entirely of epithelial cells. There are no blood vessels in the epidermis.
The dermis is the middle layer and contains many of the blood vessels, nerve endings and glands while the subcutaneous is the innermost layer. This layer is a combination of elastic, fibrous and adipose tissues.
7. Nervous system- This is a very complex system by which all parts of the body are controlled. It is made up of the brain, spinal cord and nerves. It also includes special sense organs such as the eyes, ears and taste buds.
In itself, the nervous system is broken up into the central and peripheral nervous systems. The central nervous system is made up of the brain and spinal cord. The peripheral nervous system is made up of cranial and spinal nerves. There are twelve cranial nerves that carry messages to and from the brain. The spinal nerves are those that carry messages to and from the spinal cord.
8. Excretory (urinary) system – The excretory or urinary system is mainly comprised of the kidneys, the ureters, the bladder and the urethra. It the urinary system that filters out toxins and certain waste products that the blood has taken from the cells. Although certain toxins and waste products are also gotten rid of through the digestive and respiratory systems, they are considered separate systems.
9. Reproductive system- The reproductive system includes the external and internal organs as well as related inner structures that are required for the reproduction of another human being. These organs include the ovaries, testes, fallopian tubes, vas deferens, uterus, prostrate, urethra, penis, vagina, clitoris, vulva and labia.
10. Endocrine system- Although there are few parts to the endocrine system it is vital to the health of the individual. It is made up of organs called endocrine glands that produce hormones. These hormones in turn regulate growth, use of food within the cells and reproduction. The thyroid and pituitary glands are the two main endocrine glands.
It is through these ten specialized systems all working together that allows us to maintain every aspect of life from standing to sleeping to breathing. If any one of these systems fail, the entire individual suffers.